Adaptive spatial variant interpolation for image upscaling

ABSTRACT

This disclosure describes adaptive spatial variant interpolation (SVI) techniques for image upscaling. In various embodiments, the interpolation techniques described in this disclosure may support low complexity upscaling of image while promoting high image quality, including enhanced sharpness, higher contrast and more accurate interpolation. The interpolation techniques may be applied using generalized finite impulse response (FIR) filters. In some embodiments, the interpolation techniques may be content-adaptive to provide more accurate interpolation while suppressing significant artifacts associated with sharp edges. In addition, the interpolation techniques may be readily applicable to upscaling of color imagery and video, e.g., in both YCbCr (luminance, blue chrominance, red chrominance) and RGB (red, green, blue) formats.

TECHNICAL FIELD

The disclosure relates to imaging and, more particularly, tointerpolation techniques for image scaling.

BACKGROUND

Display devices present a variety of image information, including imageinformation captured by digital video or still photo cameras, imageinformation produced by software applications, video games, or otherprograms, image information obtained from video or still photo archives,or image information obtained from broadcast or streaming media. Adisplay device may be integrated with, coupled to, or otherwiseassociated with a variety of devices, such as desktop or laptopcomputers, computer workstations, mobile devices such as personaldigital assistants (PDAs) or mobile telephones, and dedicated viewingstations such as televisions. A display device may comprise a liquidcrystal display (LCD), a cathode ray tube (CRT) display, a plasmadisplay, a projection display, or the like.

A display device maintains an inherent maximum resolution limited by thenumber of pixels capable of displaying the image information. Ingeneral, displays may produce a range of image resolution at or belowthe inherent maximum resolution. If the image information defines valuesfor less than all of the display pixels, however, the device may scalethe image information upward to a larger resolution. For example, adisplay device may produce additional pixels by interpolation to scalethe image information to a larger format. As displays become larger,image scaling becomes increasingly important. For mobile applications,even though users may desire larger displays, channel limitations tendto reduce the amount of image information that can be transmitted to amobile device, resulting in smaller format images. Hence, toconsistently achieve larger formats, image upscaling is desirable formobile applications.

Many techniques currently exist to interpolate pixel values to achieveimage upscaling. Common interpolation techniques include bilinearinterpolation, bicubic interpolation, cubic spline interpolation, andnew edge directed interpolation (NEDI). While all of the aboveinterpolation techniques are effective in upscaling the imageinformation, artifacts such as blurring may result. In addition, sometechniques, such as NEDI, may require complex calculations that consumean excessive amount of system resources, especially in small mobiledevices. Further, some existing interpolation techniques may beunsuitable for color image information, resulting in color bleeding orother artifacts. In general, upscaling is challenging because morepixels have to be created by interpolating existing but limitedinformation, possibly leading to blurriness in the output.

SUMMARY

This disclosure describes adaptive spatial variant interpolation (SVI)techniques for image upscaling. In various embodiments, theinterpolation techniques described in this disclosure may support lowcomplexity upscaling of image information while promoting high imagequality, including enhanced sharpness, higher contrast and accurateinterpolation. The interpolation techniques may be applied usinggeneralized finite impulse response (FIR) filters. In some embodiments,the interpolation techniques may be content-adaptive to provide accurateinterpolation while suppressing significant artifacts associated withsharp edges. In addition, the interpolation techniques may be readilyapplicable to upscaling of color imagery and video, e.g., in both YCbCr(luminance, blue chrominance, red chrominance) and RGB (red, green,blue) formats.

In one embodiment, the disclosure provides a method comprisingdetermining a symmetry (A) of a scaled pixel in an image based oncontent characteristics of neighboring pixels in the image, determiningan intensity (k) of a spatial variant interpolation filter based on thesymmetry A, adjusting the spatial variant interpolation filter based onthe intensity (k), and applying the spatial variant interpolation filterto interpolate the scaled pixel. In some embodiments, adjusting thespatial variant interpolation filter may include determining a warpeddistance (s′) based on the symmetry (A) of the scaled pixel and theintensity (k) of the filter response, and adjusting the spatial variantinterpolation filter based on the warped distance (s′).

In another embodiment, the disclosure provides a device comprising amemory that stores an image, and a processor that determines a symmetry(A) of a scaled pixel in an image based on content characteristics ofneighboring pixels in the image, determines an intensity (k) of aninterpolation filter based on the symmetry A, adjusts the interpolationfilter based on the intensity (k), and applies applying the spatialvariant interpolation filter to interpolate the scaled pixel. In someembodiments, the processor may determine a warped distance (s′) based onthe symmetry (A) of the scaled pixel and the intensity (k) of the filterresponse, and adjust the spatial variant interpolation filter based onthe warped distance (s′).

The techniques described in this disclosure may be implemented in ahardware, software, firmware, or any combination thereof. If implementedin software, the software may be executed in a processor, such as adigital signal processor (DSP). The software that executes thetechniques may be initially stored in a computer readable medium andloaded and executed in the processor. Accordingly, this disclosure alsocontemplates a computer readable medium comprising instructions toperform adaptive spatial variant interpolation techniques for imageupscaling.

The details of one or more embodiments of the disclosure are set forthin the accompanying drawings and the description below. Other featuresand advantages of the disclosure will be apparent from the descriptionand drawings, and from the claims.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a block diagram illustrating an exemplary mobile device thatdisplays image information that is upscaled according to the techniquesdescribed herein.

FIG. 2 is a block diagram illustrating the mobile device of FIG. 1 infurther detail.

FIGS. 3A and 3B are plots illustrating interpolation of a pixel based onadjacent pixels.

FIG. 4 is a flowchart illustrating exemplary operation of the displayprocessor of FIG. 2 in adaptively upscaling image information togenerate upscaled image information.

FIGS. 5A and 5B are graphs illustrating exemplary one-dimensional pixelarrangements, in which the display processor of FIG. 2 interpolates thevalue f(x) of a scaled pixel (x).

DETAILED DESCRIPTION

FIG. 1 is a block diagram illustrating an exemplary mobile device 10that displays image information 12 that is upscaled according to theinterpolation techniques described in this disclosure. As shown in FIG.1, mobile device 10 includes a memory 14, a display processor 16, and adisplay 18. The features illustrated in FIG. 1 may be realized by anysuitable combination of hardware and/or software components. Depictionof different features as units is intended to highlight differentfunctional aspects of mobile device 10 and does not necessarily implythat such units must be realized by separate hardware and/or softwarecomponents. Rather, functionality associated with one or more units maybe integrated within common hardware and/or software components.Moreover, while described in reference to mobile device 10, otherdevices such as personal computers, laptops, workstations, and networkeddevices may employ the image upscaling techniques described in thisdisclosure. Thus, the disclosure should not be limited to the exemplaryembodiment of mobile device 10.

In general, mobile device 10 is configured to apply adaptive spatialvariant interpolation (SVI) techniques for image upscaling. In variousembodiments, the interpolation techniques applied by mobile device 10may support low complexity upscaling of image information whilepromoting high image quality, including enhanced sharpness, highercontrast and accurate interpolation. As will be described, theinterpolation techniques may be applied using generalized finite impulseresponse (FIR) filters. In some embodiments, the interpolationtechniques may be content-adaptive to provide accurate interpolationwhile suppressing significant artifacts associated with sharp edges. Inaddition, the interpolation techniques may be applicable to upscaling ofcolor imagery and video. For example, the interpolation techniques maybe applicable to color images and video in both YCbCr (luminance, bluechrominance, red chrominance) and RGB (red, green, blue) formats.

As will be described, in some embodiments, display processor 16 may beconfigured to adapt the intensity (k) of a filter response based on aplurality of neighboring pixels. The display processor 16 may firstdetermine the symmetry (A) of a scaled pixel, i.e., a pixel thatrequires interpolation to determine its value, based on a plurality ofneighboring pixels within the image information. Next, display processor16 determines the intensity (k) of the filter response for the scaledpixel based on the symmetry (A) of the scaled pixel. Third, the displayprocessor 16 determines a warped distance (s′) based on the symmetry (A)of the scaled pixel and the intensity (k) of the filter response.

Display processor 16 then applies the filter based on the determinedwarped distance (s′) to perform spatial variant interpolation todetermine the value of the scaled pixel. Because the adaptive upscalingtechniques enable display processor 16 to adapt the intensity (k) of thefilter response based on the values of the neighboring pixels, thedisplay processor may generate upscaled image information, whichincludes the scaled pixel, with relatively higher clarity when comparedto other upscaling techniques.

The adaptive upscaling techniques also may enable display processor 16to upscale image information encoded according to one of a plurality ofcolor formats. For example, if the image information is encodedaccording to the RGB color format, display processor 16 may determinethe warped distance (s′) for the green (G) channel based on the symmetry(A) and the intensity (k). After making this determination, displayprocessor 16 may apply the filter to interpolate the red (R), green (G),and blue (B) channel values of the scaled pixel based on the warpeddistance (s′) determined for the green (G) color channel. As anotherexample, if the image information is encoded according to the YCbCrcolor format, display processor 16 may determine the warped distance(s′) for only the luminance (Y) color channel and apply the filter toonly the Y channel to interpolate the Y channel value for the scaledpixel.

Mobile device 10 may be a mobile radiotelephone or satellite telephone,a personal digital assistant, or any other type of mobile device capableof manipulating and displaying image information. Mobile device 10 maybe equipped with wireless and/or wired communication capabilities toreceive and, optionally, transmit voice, video and/or data information.Processor 16 may be integrated with a modem that also handlesdemodulation and decoding of received image information, and optionallyencoding and modulation of transmitted information.

Accordingly, mobile device 10 also may include appropriate transmit andreceive electronics, e.g., for radio frequency, satellite, or infraredcommunication. Such electronics may include suitable filters,amplifiers, frequency upconverters, frequency downconverters, diplexers,and the like. Although mobile devices are described in this disclosurefor purposes of illustration, the adaptive spatial variant interpolationtechniques may be applicable to other devices that are not generallyconsidered mobile, such as televisions, desktop computers, computerworkstations, and the like.

In some embodiments, mobile device 10 may comprise an image capturedevice to capture image information as digital videos or digital stillpictures. The image capture device may be a digital video camera, adigital still image camera, or a combination of both, and in theseinstances, the image capture device may be incorporated into mobiledevice 10, such as a mobile cellular telephone, to form a so-calledcamera phone or video phone. The image capture device preferably isequipped to capture color imagery, black-and-white imagery, or both. Inthis disclosure, the terms “image,” “imagery,” “image information,” orsimilar terms may interchangeably refer to either video or stillpictures.

With further reference to FIG. 1, memory 14 stores image information 20.Memory 14 may comprise any combination of static memory, such as aRead-Only Memory (ROM), an Electronically Programmable ROM (EPROM), aflash memory, a hard drive, and dynamic memory, such as a Random AccessMemory (RAM), a Dynamic Random Access Memory (DRAM), a Static RandomAccess Memory (SRAM), and a cache. Image information 20 may compriseinformation captured by a digital video or still camera, informationgenerated by an application, video game or other software program, orinformation obtained via broadcast or streaming media. Image information20 may define values for pixels at a specified resolution, which may beless or greater than the resolution of display 18. Typically, however,image information 20 defines pixels values at a resolution lower thanthe maximum resolution of display 18.

Display processor 16 is coupled to memory 14 and display 18, e.g., via asystem bus, memory bus, peripheral bus, or a combination thereof. Insome embodiments, display processor 16 may take the form of a hardwareaccelerator embedded within a mobile station modem (MSM), and beresponsible for transferring an upscaled image from an MSM memorysubsystem to display 18. Also, in some embodiments, memory 14 may beembedded within display processor 16, such that memory 14 becomes amemory subsystem of display processor 16. Display processor 16 isresponsible for transferring an updated image from memory 14 to display18. Display processor 16 performs a set of operations on imageinformation 20 obtained from a video or still photo capture device, fromsoftware applications, video games, or other programs, from a video orstill picture archive, or from broadcast or streaming media. Exemplaryoperations include rotation, flipping, scaling, color conversion, gammacorrection, blending, dithering, and other enhancements. Functionalunits for performing interpolation and other operations, such as thosedescribed above, may reside within a so-called video front end (VFE) ofmobile device 10.

Processor 16 may be realized by one or more microprocessors, digitalsignal processors (DSPs), application specification integrated circuits(ASICs), field programmable gate arrays (FPGAs), or any other equivalentdiscrete or integrated logic circuitry. While not shown in FIG. 1,mobile device 10 may comprise a programmable processor capable ofexecuting instructions that cause the program to execute the upscalingtechnique herein described, and processor 16 may represent a portion ofsuch programmable processor. Accordingly, the disclosure alsocontemplates a computer-readable medium comprising instructions to causea processor to perform techniques as described herein.

As described in more detail below, processor 16 applies spatial variantinterpolation filter to image information 20 to generate upscaled imageinformation 12 for display on display 18. Upscaling permits the imageinformation 20 to be displayed at a higher resolution and larger sizeformat. As examples, image information 20 can be spatially scaled upwardfrom quarter common intermediate format (QCIF) to common intermediateformat (CIF), from CIF to video graphics array (VGA), and/or from VGA tosuper VGA (SVGA). In this manner, a smaller image may be upscaled byspatial variant interpolation to provide a larger image for presentationon display 18. At the same time, interpolation techniques as describedherein may be applied to maintain quality and reduce undesirableartifacts in the upscaled image.

To upscale image information 20, display processor 16 applies a filterfirst along the rows of the pixel values defined by image information 20and second along the columns of the pixel values defined by imageinformation 20. As it applies the filter, display processor 16determines a symmetry (A) for the pixel value to be interpolated, i.e.,a scaled pixel, based on a plurality of neighboring pixels within imageinformation. The neighboring pixels may be selected to be within apredetermined distance of the pixel to be interpolated. Hence, the pixelto be interpolated is not originally present in the image data and needsto be interpolated based on pixels that are originally present in theimage data. Interpolation of the pixel adds a pixel that increases theresolution of the image. A pixel to be interpolated may be referred toas the interpolated pixel or a scaled pixel. Interpolation of multiplepixels increases the overall resolution of the image and may permitspatial upscaling.

Next, display processor 16 determines an intensity (k) of the filterresponse for the scaled pixel based on the symmetry (A) of the scaledpixel and subsequently determines a warped distance (s′) based on thesymmetry (A) of the scaled pixel and the intensity (k) of the filterresponse. During this process, display processor 16 tailors or “adapts”the filter to the content of image information 20, and more specificallyto the values of the neighboring pixel values defined by imageinformation 20. After adapting the filter, display processor 16 appliesthe filter based on the determined warped distance (s′) to performspatial variant interpolation (SVI) to determine the value of the scaledpixel.

Display processor 16 may determine the number of pixels values tointerpolate by comparing the resolution of display 18 with that of imageinformation 20. The difference between the display resolution and theresolution of image information 20 determines the amount of upscalingneed to achieve the display resolution. After interpolating the value ofeach scaled pixel, display processor 16 stores these scaled pixel valueswith original pixel values defined by image information 20 as upscaledimage information 12. In some embodiments, display processor 16 does notstore these scaled pixel values but transmits these scaled pixel valuesas well as the original pixel values defined by image information 20 todrive display 18 as the scaled pixel values are determined. Uponcompleting the upscaling, display processor 16 transmits upscaled imageinformation 12 to display 18 for display to the user.

Display 18 may comprise one of any of a variety of displays including aliquid crystal display (LCD), a cathode ray tube (CRT) display, a plasmadisplay, a projection display, and any display capable of displayingupscaled image information 12. Display 18 may be integrated with orcoupled to device 10. Display 18 maintains an inherent displayresolution controlled by the set number of pixels to display an image.Exemplary resolutions defined by the number of pixel columns by thenumber of pixel rows include 800 by 600 pixels, 1024 by 768 pixels, 1280by 768 pixels, 1280 by 800 pixels, 1280 by 1024 pixels, 1600 by 1200pixels, 1680 by 1050 pixels, 1920 by 1200 pixels, and any otherarrangement of pixels. In some embodiments, a user of mobile device 10may select one of a plurality of resolutions for display 18 so long asthe selected resolution does not exceed the inherent maximum resolutionof display 18. In other embodiments, a designer may hard-code aresolution for display 18, and typically selects the inherent maximumresolution as the hard-coded resolution.

The upscaling techniques described herein allow mobile device 10 toperform relatively low complexity linear interpolation that yieldsupscaled image information 12 of relatively high clarity, i.e., withrelatively little blurriness. The upscaling technique implemented bymobile device 10 is of low complexity because it implements a linearinterpolation method instead of more computationally intensiveinterpolation methods, such as NEDI. Moreover, the upscaling techniquesenable mobile device 10 to produce this high clarity result, in part,because it enables mobile device 10 to adapt the intensity (k) of thefilter response to the plurality of neighboring pixel values of imageinformation 20, providing content-adaptive interpolation. Thus, thistechnique allows mobile device 10 to determine some of the scaled pixelvalues according to one intensity k while determining other of thescaled pixel values according to another intensity k′, as indicated bydifferent groups of pixels that are neighbors to the particular pixel tobe interpolated. Therefore, unlike some scaling techniques that define aconstant, i.e., fixed, intensity for the filter response over the entireexpanse of image information, the upscaling technique described hereinadapts the intensity k to characteristics of image information 20 toprovide higher clarity upscaled image information 12.

FIG. 2 is a block diagram illustrating mobile device 10 of FIG. 1 infurther detail. As described above in reference to FIG. 1, mobile device10 of FIG. 2 similarly includes memory 14, display processor 16, anddisplay 18. Memory 14 stores image information 20. As illustrated inFIG. 2, display processor 16 includes symmetry module 24, lookup tables26, warped distance module 28, and Finite Input Response (FIR) filter30. While described below in reference to components 24, 26, 28 and 30,a single component or a plurality of components, such as shown in FIG.2, may perform the operations ascribed to components 24-30. Also,depiction of components 24-30 is intended to highlight differentfunctional aspects and should not necessarily be construed asrepresenting separate hardware and/or software components.

A four-tap FIR filter for use as filter 30 will be described for purposeof illustration. The pixel to be interpolated, denoted by x, iscalculated based on four original pixels, denoted by x_(n+1), x_(n−1),x_(n+2), and x_(n). For a row of pixels, the indices n+1 and n+2 maydenote pixels to the right of the pixel x to be interpolated, while theindices n and n−1 may denote pixels to the left of the pixel x to beinterpolated. The value (amplitude or intensity) of the interpolated andoriginal pixels is denoted by f(x). Using an FIR filter, the value ofthe interpolated pixel x is obtained by:

f(x)=F[s, f(x _(n−1)), f(x _(n)), f(x _(n+1)), f(x _(n+2))],  (1)

where F[•] is a linear function, and s is the phase parameter: s=x−x_(n)(0≦s≦1, by defining the distance between two adjacent original pixels tobe 1). This generalized function applies to any four-tap FIR filter,including bilinear (although it has only two taps), bicubic,cubic-spline, and the like. For example, for upscaling at a ratio of 2,a single sample needs to be interpolated so that s=½. For an upscalingratio of 4, there are three samples to interpolate and s=0.25, 0.5 and0.75 for the three interpolated pixels, respectively.

Advantages of an FIR filter include simplicity, low computationalcomplexity and capability of maintaining the values of the originalsamples. An FIR filter can be used for non-integer ratio scaling bysimply adjusting the values of s. The value of s may be quantized intomultiple levels (e.g., 32) between 0 and 1. Also, the coefficients forf(x_(n−1)), f(x_(n)), f(x_(n+1)), f(x_(n+2)) at different interpolationphases can be pre-programmed.

For an SVI technique, the distance s in equation (1) can be modifiedsuch that pixels close to edge-boundaries are interpolated in anedge-oriented fashion. Using a warped-distance (WD) scheme, an SVItechnique may be configured to apply an association rule that decidesthe side of the edge to which the interpolated pixel belongs. Anexemplary association rule is given as:

$\begin{matrix}{{A = \frac{{{{f\left( x_{n + 1} \right)} - {f\left( x_{n - 1} \right)}}} - {{{f\left( x_{n + 2} \right)} - {f\left( x_{n} \right)}}}}{L - 1}},{{{where}\mspace{14mu} L} = 256.}} & (2)\end{matrix}$

For the convenience of hardware implementation, equation (2) above canbe modified as follows:

A=(|f(x _(n+1))−f(x _(n−1))|−|f(x _(n+2))−f(x _(n))|)>>8.  (3)

Equation (3) represents a simple rule of measuring the uniformity ofpixel values on either side of an edge. If|f(x_(n+1))−f(x_(n−1))|≧|f(x_(n+2))−f(x_(n))|, the edge is morehomogenous on the right side and the pixel to be interpolated should beassociated with the right side. In this case, for a four-tap filter,more weight should be put on x_(n+1), x_(n+2). On the other hand, if|f(x_(n+1))−f(x_(n−1))|≦|f(x_(n+2))−f(x_(n))|, then the edge is morehomogenous on the left side and the pixel to be interpolated should beassociated with the left side. In this case, for a four-tap filter, moreweight should be placed on x_(n), x_(n−1).

With further reference to FIG. 2, symmetry module 16 determines thesymmetry (A) of a scaled pixel, i.e., the pixel x to be interpolated,based on a plurality of neighboring pixels within image information 20.As an example, symmetry module 16 may determine the symmetry accordingto equation (3) above. In equation (3) above, the plurality ofneighboring pixels comprise pixels denoted by x_(n+1), x_(n−1), x_(n+2),and x_(n), and f(x_(n+1)), f(x_(n−1)), f(x_(n+2)), and f(x_(n)) denotethe values associated with the respective pixels x_(n+1), x_(n−1),x_(n+2), and x_(n). Lookup tables 26 store an association between zonesof symmetry (“zones”), denoted by A₀-A_(n), and predefined intensityvalues, denoted by k₀-k_(n). The n indices for x and A are different.Lookup tables 26 merely represent one type of data structure by whichthe association may be stored, and other data structures, such as linkedlists, hash tables, trees, and binary trees, may store this association.Lookup tables 26 may store the association in a manner represented bythe following equations (4):

k=k₀, for 0≦|A|<A ₁;

k=k₁, for A ₁ ≦|A|<A ₂;

. . .

k=k_(n−1), for A _(n−1) ≦|A|≦1,  (4)

-   -   where 0<A₁<A₂< . . . <A_(n−1)<1.        In equations (4) above, k represents the intensity of the filter        response, k₀-k_(n) denote predefined intensity values, and        A₀-A_(n) denote the edges of the zones of symmetry. The value k        is varied based on the value of A, per equation (4), providing        adjustment of the spatial variant interpolation filter response        based on content characteristics of the image. In some        embodiments, the k value may be selectively adjusted based on        the A value in normal cases, or based on a fixed value if        computational resources to compute A are scarce. As k is        adaptive as a function of A, there may be different k values        within the same image or video frame for different pixels to be        interpolated. Notably, the value A may be expressed as an        absolute value as it could be positive or negative.

In some embodiments, a frame may be characterized by a k map thatassigns different values of k, e.g., to different areas, regions, pixelgroups, or pixels. Hence, a frame may be pre-processed to determinevalues of k for predetermined regions. Then, the k value can be used forspatial variant interpolation for upscaled pixels, i.e., pixels to beinterpolated, in each of those respective regions. In particular, thespatial variant interpolation technique may reference the k map todetermine the particular k for a region as it produces one or moreinterpolated pixels in that region.

A designer may predefine lookup tables 26 by specifying values fork₀-k_(n) and A₀-A_(n). In some embodiments, however, display processor16 automatically adapts either or both of k₀-k_(n) and A₀-A_(n) to oneor more exemplary conditions, such as the quality of image information20 being upscaled, the identity or type of application requestingdisplay 18 to display image information 20, and the level of availablesystem resources within mobile device 10. Moreover, lookup tables 26 maycomprise one or more lookup tables, or more generally, data structures,that store one or more associations. Display processor 16 may associateeach of these independent lookup tables 26 with a different applicationthat requests display 18 to display image information 20. Alternatively,display processor 16 may associate each of these independent lookuptables 26 with a varying level of system resource use and/or quality ofimage information 20.

Warped distance module 28 determines a warped distance (s′) based on thesymmetry (A) of the scaled pixel and the intensity (k) of the filterresponse from symmetry module 24 and lookup tables 26. Warped distancemodule 28 may determine the warped distance (s′) according to thefollowing equation (5):

s′=s−kAs(s−1)  (5)

where s denotes the distance of the scaled pixel to one of the pluralityof neighboring pixels, A denotes the symmetry of the scaled pixel, and kdenotes the intensity of the filter response for the scaled pixel. Thevalue s′ provides a phase modification as a function of s, A and k. Inturn, the value k is modified as a function of A. In some scenarios, ifk is set to 0, the interpolation technique reverts to spatial invariantinterpolation. Otherwise, varying values of k result in varying valuesof s′, and drive content-adaptive spatial variant interpolation(CA-SVI). The distance (s) between the scaled pixel to one of theplurality of neighboring pixels may be defined by either of thefollowing equations (6):

s=x−x _(n),

1−s=x _(n+1)  (6)

where x denotes the position of the scaled pixel, x_(n) denotes theposition of the pixel to the left of the scaled pixel along the x-axis,and x_(n+1) denotes the pixel to the right of the scaled pixel along thex-axis. As shown by equation (6), the distance between each pixel x_(n)and x_(n+1) has been normalized to one.

Warped distance module 28 may determine the warped distance (s′) forinstances where image information 20 includes color image information20. If color image information 20 is encoded according to the RGB colorformat, for example, warped distance module 28 computes the warpeddistance (s′) for the green (G) channel only and transmits this warpeddistance (s′) for the green (G) channel to FIR filter 30 wheninterpolating all three color channel values, i.e., green (G), red (R),and blue (B) channels, of the scaled pixel. If color image information20 is encoded according to the YCbCr color format, however, warpeddistance module 28 computes the warped distance (s′) for only theluminance (Y) channel and transmits this warped distance (s′) for theluminance (Y) channel to FIR filter 30 when interpolating the luminance(Y) channel value of the scaled pixel.

FIR filter 30 applies a filter based on the determined warped distance(s′) to perform spatial variant interpolation to determine the value ofthe scaled pixel. FIR filter 30 may apply a filter as described by thefollowing equation (7) below:

$\begin{matrix}{{f(x)} = {{\frac{1}{2}\left( {{- s^{\prime 3}} + {2s^{\prime 2}} - s^{\prime}} \right){f\left( x_{n - 1} \right)}} + {\frac{1}{2}\left( {{3s^{\prime 3}} - {5s^{\prime 2}} + 2} \right){f\left( x_{n} \right)}} + {\frac{1}{2}\left( {{{- 3}s^{\prime 3}} + {4s^{\prime 2}} + s^{\prime}} \right){f\left( x_{n + 1} \right)}} + {\frac{1}{2}\left( {s^{\prime 3} - s^{\prime 2}} \right){f\left( x_{n + 2} \right)}}}} & (7)\end{matrix}$

where f(x) denotes the value of the scaled pixel, s′ denotes the warpeddistance, the plurality of neighboring pixels comprise pixels denoted byx_(n+1), x_(n−1), x_(n+2), and x_(n), and f(x_(n+1)), f(x_(n−1)),f(x_(n+2)), and f(x_(n)) denote the value associated with the respectivepixels x_(n+1), x_(n−1), x_(n+2), and x_(n). Equation (7) describesspatial-variant bicubic interpolation that is content adaptive, ormerely “adaptive,” because the intensity (k) of the filter response,which factors into the warped distance (s′), varies according to thevalues of the surrounding plurality of neighboring pixels, f(x_(n+1)),f(x_(n−1)), f(x_(n+2)), and f(x_(n)). Although described herein inreference to spatial-variant bicubic interpolation, the upscalingtechniques described herein may allow for other levels of interpolation,such as bilinear interpolation, e.g., as described by equation (8)below:

f(x)=(1−s′)f(x _(n))+s′f(x _(n+1))  (8)

FIR filter 30 may also offer flexibility in that it may not always applyspatial-variant interpolation, but rather the more typicalspatial-invariant bicubic interpolation in some circumstances. If one ofthe above lookup tables 26 specifies an intensity value equal to zero,whereupon the intensity (k) of the filter response is set to zero andthe warped distance (s′) therefore equals the distance (s), FIR filter30 applies a spatial-invariant bicubic filter according to equation (7)with s substituted for s′. Therefore, FIR filter 30 may adapt in such amanner as to perform spatial-invariant bicubic interpolation to imageinformation 20 and such adaptation may occur after determining thequality of image information 20, the identity of an application thatrequested display 18 to display image information 20, and/or theavailable system resources of mobile device 10, as described above. Inother words, in some cases, FIR filter 30 may be configured to applyspatial variant interpolation, but be adaptive to switch to spatialinvariant interpolation under certain conditions.

As an illustration, the following values of k could be used fordifferent absolute values of A to trigger either spatial variantinterpolation or spatial invariant interpolation:

k=4, for 0≦|A|<0.45;

k=0, for 0.45≦A|<1.  (9)

FIGS. 3A and 3B are plots illustrating interpolation of a pixel value xbased on values of adjacent pixels x_(n−1), x_(n), x_(n+1), x_(n+2).FIGS. 3A and 3B illustrate plotting of pixel samples for the abovevalues of k set forth in equation (9) when the absolute value of A=0 andthe absolute value of A=0.75, respectively. With the samples plotted asin FIG. 3A, A=0 and k=4. Hence, for the example of FIG. 3A, spatialvariant interpolation (SVI) is to be used. With the samples plotted asin FIG. 3B, however, |A|=0.75, and k=0. In this case, when k=0, spatialinvariant interpolation is to be used instead of spatial variantinterpolation (SVI).

The embodiment illustrated in FIG. 2 is for exemplary purposes only.Display processor 16 need not reside within display processor 16 ofmobile device 10 and may reside within any device capable of storing,manipulating, and generating image information. As described above,display processor 16 may perform upscaling according to the hereindescribed upscaling techniques, thereby offering mobile device 10 arelatively low complexity method to generate relatively high clarityupscaled image information 12.

FIG. 4 is a flowchart illustrating exemplary operation of displayprocessor 16 of FIG. 2 in adaptively upscaling image information 20 togenerate upscaled image information 12 using interpolation techniques asdescribed in this disclosure. Initially, a designer may configure lookuptables 26, or some other data structure as described above, to store anassociation between zones of symmetry (A₀-A_(n)) with intensity values(k₀-k_(n)). The designer may also select which method of interpolation,i.e., either bilinear or bicubic interpolation, display processor 16should apply to image information 20.

Once configured, mobile device 10 may interact with a user (not shown),whereupon the user may interact with one or more software programs, suchas an application or game, and/or hardware components, such as a digitalvideo camera or digital still image camera component. Through thisinteraction, the software program and/or hardware component may storeimage information 20 to memory 14, and display processor 16 may retrieveimage information 20 from memory 14 for display on display 18 (32).

Upon retrieving image information 20, display processor 16 may perform afinal set of operations, as described above. In particular, displayprocessor 16 may upscale image information 20 according to the upscalingtechnique described herein. First, symmetry module 24 of displayprocessor 16 may determine the symmetry (A) of the scaled pixel based onthe neighboring pixel values (34). Symmetry module 24 may determine thesymmetry (A) according to above equation (1) and as described below inreference to FIGS. 5A and 5B. Next, symmetry module 24 accesses lookuptables 26 to determine the associated intensity value (k₀-k_(n)) thatcorresponds to the zone of symmetry (A₀-A_(n)) in which the symmetry (A)lies.

In the example of FIG. 4, two zones of symmetry exist and are defined byA₀=0.45. Thus, modifying equation (2) to this specific configurationprovides equation (9) above, which describes the association stored inone of lookup tables 26, and is again reproduced below:

k=4, for 0≦|A|<0.45;

k=0, for 0.45≦|A|<1.  (9)

Here, as mentioned above, the intensity k of the filter response equalsthe intensity value k₀, which equals 4, if the symmetry A is greaterthan or equal to 0 and less than A₀, which equals 0.45. The intensity kequals the intensity value k₁, which equals 0, if the symmetry A isgreater than or equal to A₀, which equals 0.45, but less than 1. Becausethe symmetry A must lie between 0 and 1, only A₀ is required todelineate two zones of symmetry, and display processor 16 only needs todetermine whether it lies within the first zone of symmetry (36). Whiledescribed in reference to two zones of symmetry, two or more zones ofsymmetry may exist, as shown by equation (4), and the upscalingtechnique described herein should not be limited to strictly two zonesof symmetry. The number and size of zones may be adaptive in someembodiments, e.g., based on availability of computing resources andother performance characteristics.

If the symmetry (A) lies within the first zone of symmetry (“YES” 36),i.e., 0≦A<0.45, lookup table 26 returns intensity value k₀, or 4, towarped distance module 28, which in turn sets the intensity k equal to 4(38). After setting the intensity (k) to 4, warped distance module 28determines the distance (s) between the scaled pixel and the neighboringpixels (40). Warped distance module 28 may compute the distance (s)according to equation (4) above. If image information 20 is encodedaccording to the RGB color format (“YES” 42), warped distance module 28determines the warped distance (s′) for the green (G) channel (44).Warped distance module 28 may compute the warped distance (s′) for thegreen (G) channel according to the above equation (3). Warped distancemodule 28 sets the warped distance (s′) for each of the red (R) and blue(B) channels equal to the warped distance (s′) computed for the green(G) channel (46). The green (G) channel may be chosen to determine thephase modification term s′ to avoid gray imbalance and use the channelthat appears most intense to the human eye.

If image information 20 is not encoded according to the RGB color formatbut according to the YCbCr color format (“NO” 42), warped distancemodule 28 determines the warped distance (s′) only for the luminance (Y)channel of image information 20 (48). While only the RGB and YCbCr colorformats are discussed herein, other color formats may cause warpeddistance module 28 to compute warped distances for varying channels ofthese other color formants, and the upscaling technique described hereinshould not be strictly limited to the RGB and YCbCr color formats.

After determining the warped distance(s) (s′), warped distance module 28provides the warped distance(s) (s′) to FIR filter 30. FIR filter 30performs content adaptive spatial variant bicubic interpolation (50) viaapplication of a filter that may conform to that described above byequation (5). FIR filter 30 performs this adaptive spatial variantbicubic interpolation on one or more channels of image information 20 togenerate a scaled pixel value of upscaled image information 16. Forexample, if image information 20 is encoded according to the RGB colorformat, FIR filter 30 may perform this interpolation on the red (R),green (G), and blue (B) channels of image information 20, but uses onlythe warped distance (s′) determined for the green (G) channel.Interpolating all three RGB channels according to the warped distance(s′) determined for the green (G) channel typically lessens thelikelihood of color bleeding in upscaled image information 12. Asanother example, if image information 20 is encoded according to theYCbCr color channel, FIR filter 30 may perform this interpolation ononly the luminance (Y) channel of image information 20. FIR filter 30only interpolates the Y channel in this example because it represents atrue color intensity value while both the chromatic blue (Cb) andchromatic red (Cr) channels represent offsets and not true color values.

If, however, the symmetry lies within the second zone (“NO” 36), i.e.,0.45≦A<1, lookup table 26 returns intensity value k₁, or 0, to warpeddistance module 28, which in turn sets the intensity k equal to 0 (52).After setting the intensity (k) to 0, warped distance module 28determines the distance (s) between the scaled pixel and the neighboringpixels (54). Warped distance module 28 may compute the distance (s)according to equation (4) above. In this instance, because k equals 0,warped distance module 28 may immediately set the warped distance (s′)equal to zero (0) (56). Warped distance module 28 may compute the warpeddistance (s′) according to the above equation (3), which when k equals0, reduces equation (3) to s′=s.

When s′ equals s, FIR filter 30 performs spatial invariant bicubicinterpolation (58), i.e., rather than spatial variant interpolation, viaapplication of a filter that may be described by the above equation (5).Via application of the filter, FIR filter 30 generates a scaled pixelvalue of upscaled image information 12.

Upon interpolating a scaled pixel value, display processor 16 determineswhether it has finished interpolating all necessary scaled pixel values(60). Typically, display processor 16 applies FIR filter 30 first alongthe rows of the pixel values defined by image information 20 and secondalong the columns of the pixel values defined by image information 20.Thus, display processor 16 finishes after applying FIR filter 30 alongthe last column of image information 20. If not finished (“NO” 60),display processor 20 applies FIR filter 30 to the next scaled pixelvalue but only after determining the symmetry (A), intensity (k),distance (s) and warped distance (s′) of this new scaled pixel (34-60).However, if finished (“YES” 60), display processor 16 may transmitupscaled image information 12 for display on display 18.

FIGS. 5A and 5B are graphs illustrating an exemplary one dimensionalpixel arrangement, in which display processor 20 of FIG. 2 interpolatesa value (f(x)) of a scaled pixel (x). FIG. 5A shows a graph 62 in whichthe scaled pixel (x) lies along an edge having a more homogenous rightside. FIG. 5B shows a graph 64 in which the scaled pixel (x) lies alongan edge having a more homogenous left side. While both of graphs 62, 64illustrate a one-dimensional pixel arrangement, this is merely exemplaryand typically image information 20 includes information relating totwo-dimensional pixel arrangements. However, because FIR filter 30 canbe applied first to rows, a one-dimensional pixel arrangement, and nextto columns, another one-dimensional pixel arrangement, it is appropriateto discuss the upscaling technique in this context.

Referring to FIG. 5A, graph 62 includes a sigmoid edge line 66 definedby pixel values 68A-68D, or f(x_(n−1)), f(x_(n)), f(x_(n+1)), andf(x_(n+2)), respectively. Graph 62 further includes scaled pixel x,which lies between pixels x_(n) and x_(n+1). In order to interpolate avalue for scaled pixel x, symmetry module 24 of display processor 16first determines the symmetry (A) of scaled pixel x according toequation (1) above. In determining the symmetry (A), symmetry module 24may compute both of |(f(x_(n+1))−f(x_(n−1))| and |f(x_(n+2))−f(x_(n))|of equation (1), which are represented in graph 62 by distance 1 (d₁)and distance 2 (d₂), respectively. If d₁ is greater than d₂, the edgehas a more homogenous right side, and the scaled pixel value should liecloser to those pixels values f(x_(n+1)) and f(x_(n+2)) of the rightside to maintain definitive edges. To obtain this result, scaled pixel xis warped closer to the right side. Warping scaled pixel x requires thatthe intensity (k) of the filter response be defined greater than or lessthan 0.

After determining the symmetry (A), symmetry module 28 accesses lookuptables 26 to determine the associated intensity value, as describedabove. If the symmetry (A) lies within the above described first zone ofsymmetry, i.e., if |d₁−d₂| is greater than or equal to 0 but less than0.45, warped distance module 28 receives the first intensity value(k₀=4) from lookup table 26 and sets the intensity k=k₀. However, if thesymmetry lies within the second zone of symmetry, i.e., if |d₁−d₂| isgreater than or equal to 0.45 but less than 1, warped distance module 28receives the second intensity value (k₁=0) from lookup table 26 and setsthe intensity k=k₁. Next, warped distance module 28 determines thedistance (s) 70 between scaled pixel x and pixel x, according to one ofequations (4) above. If the intensity k equals 4, warped pixel moduledetermines the warped distance (s′) according to the above equation (3).If the intensity k equals 0, warped pixel module determines that thewarped distance (s′) equals the distance (s) and scaled pixel x is notwarped. Upon calculating the warped distance (s′), display processor 16applies FIR filter 30 to perform either of spatial variant or spatialinvariant bicubic interpolation, as described above.

Referring to FIG. 5B, graph 64 includes a sigmoid edge line 72 definedby pixel values 74A-74D, or f(x_(n−1)), f(x_(n)), f(x_(n+1)), andf(x_(n+2)) respectively. Graph 64 further includes scaled pixel x, whichlies between pixels x_(n) and x_(n+1). In order to interpolate a valuefor scaled pixel x, symmetry module 24 of display processor 16 firstdetermines the symmetry (A) of scaled pixel x according to equation (1)above. In determining the symmetry (A), symmetry module 24 may computeboth of |(f(x_(n+1))−f(x_(n−1))| and |f(x_(n+2))−f(x_(n))| of equation(1), which are represented in graph 64 by distance 1 (d₁) and distance 2(d₂), respectively. If d₂ is greater than d₁, the edge has a morehomogenous left side, and the scaled pixel value should lie closer tothose pixels values f(x_(n−1)) and f(x_(n)) of the left side to maintaindefinitive edges. To obtain this result, scaled pixel x is warped closerto the left side. Warping scaled pixel x requires that the intensity (k)of the filter response be defined to be greater than or less than 0.

After determining the symmetry (A), symmetry module 28 accesses lookuptables 26 to determine the associated intensity value, as describedabove. If the symmetry (A) lies within the above described first zone ofsymmetry, i.e., if |d₁−d₂| is greater than or equal to 0 but less than0.45, warped distance module 28 receives the first intensity value(k₀=4) from lookup table 26 and sets the intensity k=k₀. However, if thesymmetry lies within the second zone of symmetry, i.e., if |d₁−d₂| isgreater than or equal to 0.45 but less than 1, warped distance module 28receives the second intensity value (k₁=0) from lookup table 26 and setsthe intensity k=k₁. Next, warped distance module 28 determines thedistance (s) 76 between scaled pixel x and pixel x_(n) according to oneof equations (4) above. If the intensity k equals 4, warped pixel moduledetermines the warped distance (s′) according to the above equation (5).If the intensity k equals 0, warped pixel module determines that thewarped distance (s′) equals the distance (s) and scaled pixel x is notwarped. Upon calculating the warped distance (s′), display processor 16applies FIR filter 30 to perform either of spatial variant or spatialinvariant bicubic interpolation, as described above.

This disclosure describes adaptive spatial variant interpolation (SVI)techniques for image upscaling. In various embodiments, theinterpolation techniques described in this disclosure may support lowcomplexity upscaling of image information while promoting high imagequality, including enhanced sharpness, higher contrast and accurateinterpolation. The interpolation techniques may be applied usinggeneralized finite impulse response (FIR) filters. In some embodiments,the interpolation techniques may be content-adaptive to provide accurateinterpolation while suppressing significant artifacts associated withsharp edges. In addition, the interpolation techniques may be readilyapplicable to upscaling of color imagery and video, e.g., in both YCbCr(luminance, blue chrominance, red chrominance) and RGB (red, green,blue) formats.

The upscaling techniques described herein may be implemented inhardware, software, firmware, or any combination thereof. If implementedin software, the techniques may be directed to a computer-readablemedium comprising program code providing machine-executableinstructions, that when executed in a device that captures images,performs one or more of the techniques described herein. In that case,the computer-readable medium may comprise random access memory (RAM)such as synchronous dynamic random access memory (SDRAM), read-onlymemory (ROM), non-volatile random access memory (NVRAM), electricallyerasable programmable read-only memory (EEPROM), FLASH memory, and thelike.

The program code may be stored on memory in the form of computerreadable instructions. In that case, a processor such as amicroprocessor or digital signal processor (DSP) may executeinstructions stored in memory in order to carry out one or more of thetechniques described herein. In some cases, the techniques may beexecuted by a DSP that invokes various hardware components. In othercases, the techniques described in this disclosure may be implemented bya microprocessor, one or more application specific integrated circuits(ASICs), one or more field programmable gate arrays (FPGAs), or someother hardware-software combination.

Various embodiments of the disclosure have been described. These andother embodiments are within the scope of the following claims.

1. A method comprising: determining a symmetry (A) of a scaled pixel inan image based on content characteristics of neighboring pixels in theimage; determining an intensity (k) of a spatial variant interpolationfilter based on the symmetry A; adjusting the spatial variantinterpolation filter based on the intensity (k); and applying thespatial variant interpolation filter to interpolate the scaled pixel. 2.The method of claim 1, wherein adjusting the spatial variantinterpolation filter includes determining a warped distance (s′) basedon the symmetry (A) of the scaled pixel and the intensity (k) of thefilter response, and adjusting the spatial variant interpolation filterbased on the warped distance (s′).
 3. The method of claim 2, whereindetermining the symmetry (A) of the scaled pixel comprises determiningthe symmetry (A) of the scaled pixel according to the equation:A=(|f(x _(n+1))−f(x _(n−1))|−|f(x _(n+2))−f(x _(n))|)>>8 where theneighboring pixels comprise pixels denoted by x_(n+1), x_(n−1), x_(n+2),and x_(n), and f(x_(n+1)), f(x_(n−1)), f(x_(n+2)), and f(x_(n)) denotethe value associated with the respective pixels x_(n+1), x_(n−1),x_(n+2), and x_(n).
 4. The method of claim 2, wherein determining theintensity (k) of the filter response comprises: determining whether thesymmetry (A) resides within one of a plurality of zones (A₀-A_(n));setting the intensity (k) to one of a plurality of intensity values(k₀-k_(n)) associated with the one of the plurality of zones (A₀-A_(n))in which the symmetry (A) lies.
 5. The method of claim 4, furthercomprising selectively setting the intensity (k) to equal zero such thatthe warped distance (s′) equals a distance (s) from the scaled pixel toone of the neighboring pixels to transform the spatial variantinterpolation filter into a spatial invariant interpolation filter, andapplying the spatial invariant interpolation filter to interpolate thescaled pixel.
 6. The method of claim 4, wherein setting the intensity(k) comprises: accessing one of a plurality of data structures thatstore the association of zones (A₀-A_(n)) to the plurality of intensityvalues (k₀-k_(n)) based on the determined symmetry (A) to retrieve oneof the plurality of intensity values (k₀-k_(n)); and setting theintensity (k) to the retrieved one of the plurality of intensity values(k₀-k_(n)).
 7. The method of claim 6, wherein accessing one of theplurality of data structures comprises accessing one of the plurality ofdata structures based on one or more of available system resources, anda type of an application requesting the image.
 8. The method of claim 2,wherein determining the intensity (k) of the filter response comprises:determining a quality of the image; and determining the intensity (k) ofthe filter response for the scaled pixel based on the determination ofthe quality of the image.
 9. The method of claim 2, wherein determiningthe warped distance (s′) comprises determining the warped distance (s′)according to the equation:s′=s−kAs(s−1) where s denotes the distance of the scaled pixel to one ofthe neighboring pixels, A denotes the symmetry of the scaled pixel, andk denotes the intensity of the filter response for the scaled pixel. 10.The method of claim 2, wherein determining the warped distance (s′)comprises determining the warped distance (s′) for the green (G) channelof the image encoded according to the RGB color format, and whereinapplying the filter comprises applying the filter to the red (R), green(G), and blue (B) channels based on the warped distance (s′) determinedfor the green (G) channel of the image to perform spatial variantinterpolation to determine the value of the scaled pixel.
 11. The methodof claim 2, wherein determining the warped distance (s′) comprisesdetermining the warped distance (s′) for the luminance (Y) channel ofthe image encoded according to the YCbCr color format; wherein applyingthe filter comprises applying the filter to the luminance (Y) channelbased on the warped distance (s′) determined for the luminance (Y)channel to perform spatial variant interpolation to determine the valueof the scaled pixel.
 12. The method of claim 2, wherein applying thefilter comprises applying a filter based on the determined warpeddistance (s′) to perform spatial variant bicubic interpolation todetermine the value of the scaled pixel.
 13. The method of claim 12,wherein applying the filter further comprises applying the filterdescribed by the equation:${f(x)} = {{\frac{1}{2}\left( {{- s^{\prime 3}} + {2s^{\prime 2}} - s^{\prime}} \right){f\left( x_{n - 1} \right)}} + {\frac{1}{2}\left( {{3s^{\prime 3}} - {5s^{\prime 2}} + 2} \right){f\left( x_{n} \right)}} + {\frac{1}{2}\left( {{{- 3}s^{\prime 3}} + {4s^{\prime 2}} + s^{\prime}} \right){f\left( x_{n + 1} \right)}} + {\frac{1}{2}\left( {s^{\prime 3} - s^{\prime 2}} \right){f\left( x_{n + 2} \right)}}}$where f(x) denotes the value of the scaled pixel, s′ denotes the warpeddistance, the neighboring pixels comprise pixels denoted by x_(n+1),x_(n−1), x_(n+2), and x_(n), and f(x₊₁), f(x_(n−1)), f(x_(n+2)), andf(x_(n)) denote the value associated with the respective pixels x_(n+1),x_(n−1), x_(n+2), and x_(n).
 14. The method of claim 1, furthercomprising: generating upscaled image that includes the value of thescaled pixel; and displaying the upscaled image via a display.
 15. Adevice comprising: a memory that stores an image; and a processor thatdetermines a symmetry (A) of a scaled pixel in an image based on contentcharacteristics of neighboring pixels in the image, determines anintensity (k) of an interpolation filter based on the symmetry A,adjusts the interpolation filter based on the intensity (k), and appliesthe spatial variant interpolation filter to interpolate the scaledpixel.
 16. The device of claim 1, wherein the processor determines awarped distance (s′) based on the symmetry (A) of the scaled pixel andthe intensity (k) of the filter response, and adjusts the spatialvariant interpolation filter based on the warped distance (s′).
 17. Thedevice of claim 16, wherein the processor determines the symmetry (A) ofthe scaled pixel according to the equation:A=(|f(x _(n+1))−f(x _(n−1))|−|f(x _(n+2))−f(x _(n))|)>>8 where theneighboring pixels comprise pixels denoted by x_(n+1), x_(n−1), x_(n+2),and x_(n), and f(x_(n+1)), f(x_(n−1)), f(x_(n+2)), and f(x_(n)) denotethe value associated with the respective pixels x_(n+1), x_(n−1),x_(n+2), and x_(n).
 18. The device of claim 16, wherein the processordetermines whether the symmetry (A) resides within one of a plurality ofzones (A₀-A_(n)), and sets the intensity (k) to one of a plurality ofintensity values (k₀-k_(n)) associated with the one of the plurality ofzones (A₀-A_(n)) in which the symmetry (A) lies.
 19. The device of claim16, wherein the processor selectively sets the intensity (k) to equalzero such that the warped distance (s′) equals a distance (s) from thescaled pixel to one of the neighboring pixels to transform the spatialinvariant interpolation filter into a spatial invariant interpolationfilter, and applies the spatial invariant interpolation filter tointerpolate the scaled pixel.
 20. The device of claim 18, wherein thememory stores a plurality of data structures that store an associationbetween zones of symmetry (A₀-A_(n)) and a plurality of intensity values(k₀-k_(n)), and the processor accesses one of the plurality of datastructures that stores the association of zones (A₀-A_(n)) to theplurality of intensity values (k₀-k_(n)) based on the determinedsymmetry (A) to retrieve one of the plurality of intensity values(k₀-k_(n)), and sets the intensity (k) to the retrieved one of theplurality of intensity values (k₀-k_(n)).
 21. The device of claim 20,wherein the processor accesses one of the plurality of data structuresbased on one or more of available system resources, and a type ofapplication requesting the image.
 22. The device of claim 16, whereinthe processor determines quality of the image, and determines theintensity (k) of the filter response for the scaled pixel based on thedetermination of the quality of the image.
 23. The device of claim 16,wherein the processor determines the warped distance (s′) according tothe equation:s′=s−kAs(s−1) where s denotes the distance of the scaled pixel to one ofthe neighboring pixels, A denotes the symmetry of the scaled pixel, andk denotes the intensity of the filter response for the scaled pixel. 24.The device of claim 16, wherein the processor determines the warpeddistance (s′) for the green (G) channel of the image encoded accordingto the RGB color format, and applies the filter to the red (R), green(G), and blue (B) channels based on the warped distance (s′) determinedfor the green (G) channel of the image to perform spatial variantinterpolation to determine the value of the scaled pixel.
 25. The deviceof claim 16, wherein the processor determines the warped distance (s′)for the luminance (Y) channel of the image encoded according to theYCbCr color format, and applies the filter based on the warped distance(s′) determined for the luminance (Y) channel to perform spatial variantinterpolation to determine the value of the scaled pixel.
 26. The deviceof claim 16, wherein the processor applies the filter based on thedetermined warped distance (s′) to perform spatial variant bicubicinterpolation to determine the value of the scaled pixel.
 27. The deviceof claim 26, wherein the processor applies the filter described by theequation:${f(x)} = {{\frac{1}{2}\left( {{- s^{\prime 3}} + {2s^{\prime 2}} - s^{\prime}} \right){f\left( x_{n - 1} \right)}} + {\frac{1}{2}\left( {{3s^{\prime 3}} - {5s^{\prime 2}} + 2} \right){f\left( x_{n} \right)}} + {\frac{1}{2}\left( {{{- 3}s^{\prime 3}} + {4s^{\prime 2}} + s^{\prime}} \right){f\left( x_{n + 1} \right)}} + {\frac{1}{2}\left( {s^{\prime 3} - s^{\prime 2}} \right){f\left( x_{n + 2} \right)}}}$where f(x) denotes the value of the scaled pixel, s′ denotes the warpeddistance, the neighboring pixels comprise pixels denoted by x_(n+1),x_(n−1), x_(n+2), and x_(n), and f(x_(n+1)), f(x_(n−1)), f(x_(n+2)), andf(x_(n)) denote the value associated with the respective pixels x_(n+1),x_(n−1), x_(n+2), and x_(n).
 28. The device of claim 16, furthercomprising a display to display upscaled image, wherein the processorgenerates the upscaled image that includes the value of the scaledpixel.
 29. A computer-readable medium comprising instructions forcausing a programmable processor to: determine a symmetry (A) of ascaled pixel in an image based on content characteristics of neighboringpixels in the image; determine an intensity (k) of a spatial variantinterpolation filter based on the symmetry A; adjust the spatial variantinterpolation filter based on the intensity (k); and apply the spatialvariant interpolation filter to interpolate the scaled pixel.
 30. Thecomputer-readable medium of claim 27, wherein the instructions cause theprocessor to determine a warped distance (s′) based on the symmetry (A)of the scaled pixel and the intensity (k) of the filter response, andadjust the spatial variant interpolation filter based on the warpeddistance (s′).
 31. The computer-readable medium of claim 30, wherein theinstructions cause the processor to determine the symmetry (A) of thescaled pixel according to the equation:A=(|f(x _(n+1))−f(x _(n−1))|−|f(x _(n+2))−f(x _(n))|)>>8 where theneighboring pixels comprise pixels denoted by x_(n+1), x_(n−1), x_(n+2),and x_(n), and f(x_(n+1)), f(x_(n−1)), f(x_(n+2)), and f(x_(n)) denotethe value associated with the respective pixels x_(n+1), x_(n−1),x_(n+2), and x_(n).
 32. The computer-readable medium of claim 30,wherein the instructions cause the processor to determine whether thesymmetry (A) resides within one of a plurality of zones (A₀-A_(n)), andset the intensity (k) to one of a plurality of intensity values(k₀-k_(n)) associated with the one of the plurality of zones (A₀-A_(n))in which the symmetry (A) lies.
 33. The computer-readable medium ofclaim 30, wherein the instructions cause the processor to selectivelyset the intensity (k) to equal zero such that the warped distance (s′)equals a distance (s) from the scaled pixel to one of the neighboringpixels to transform the spatial invariant interpolation filter into aspatial invariant interpolation filter, and apply the spatial invariantinterpolation filter to interpolate the scaled pixel.
 34. Thecomputer-readable medium of claim 30, wherein the instructions cause theprocessor to access one of a plurality of data structures that store theassociation of zones (A₀-A_(n)) to the plurality of intensity values(k₀-k_(n)) based on the determined symmetry (A) to retrieve one of theplurality of intensity values (k₀-k_(n)), and set the intensity (k) tothe retrieved one of the plurality of intensity values (k₀-k_(n)). 35.The computer-readable medium of claim 34, wherein the instructions causethe processor to access one of the plurality of data structures based onone or more of available system resources, and an application requestingthe image.
 36. The computer-readable medium of claim 30, wherein theinstructions cause the processor to determine the quality of the image,and determine the intensity (k) of the filter response for the scaledpixel based on the determination of the quality of the image.
 37. Thecomputer-readable medium of claim 30, wherein the instructions cause theprocessor to determine the warped distance (s′) according to theequation:s′=s−kAs(s−1) where s denotes the distance of the scaled pixel to one ofthe neighboring pixels, A denotes the symmetry of the scaled pixel, andk denotes the intensity of the filter response for the scaled pixel. 38.The computer-readable medium of claim 30, wherein the instructions causethe processor to determine the warped distance (s′) for the green (G)channel of the image encoded according to the RGB color format, andapply the filter to the red (R), green (G), and blue (B) channels basedon the warped distance (s′) determined for the green (G) channel of theimage to perform spatial variant interpolation to determine the value ofthe scaled pixel.
 39. The computer-readable medium of claim 30, whereinthe instructions cause the processor to determine the warped distance(s′) for the luminance (Y) channel of the image encoded according to theYCbCr color format, and apply the filter to the luminance (Y) channelbased on the warped distance (s′) determined for the luminance (Y)channel to perform spatial variant interpolation to determine the valueof the scaled pixel.
 40. The computer-readable medium of claim 30,wherein the instructions cause the processor to apply the filter basedon the determined warped distance (s′) to perform spatial variantbicubic interpolation to determine the value of the scaled pixel. 41.The computer-readable medium of claim 30, wherein the instructions causethe processor to apply the filter described by the equation:${f(x)} = {{\frac{1}{2}\left( {{- s^{\prime 3}} + {2s^{\prime 2}} - s^{\prime}} \right){f\left( x_{n - 1} \right)}} + {\frac{1}{2}\left( {{3s^{\prime 3}} - {5s^{\prime 2}} + 2} \right){f\left( x_{n} \right)}} + {\frac{1}{2}\left( {{{- 3}s^{\prime 3}} + {4s^{\prime 2}} + s^{\prime}} \right){f\left( x_{n + 1} \right)}} + {\frac{1}{2}\left( {s^{\prime 3} - s^{\prime 2}} \right){f\left( x_{n + 2} \right)}}}$where f(x) denotes the value of the scaled pixel, s′ denotes the warpeddistance, the neighboring pixels comprise pixels denoted by x_(n+1),x_(n−1), x_(n+2), and x_(n), and f(x_(n+1)), f(x_(n−1)), f(x_(n+2)), andf(x_(n)) denote the value associated with the respective pixels x_(n+1),x_(n−1), x_(n+2), and x_(n).
 42. The computer-readable medium of claim30, further comprising instructions that cause the processor to generateupscaled image that includes the value of the scaled pixel, drive adisplay device to display the upscaled image.
 43. A device comprising:means for determining a symmetry (A) of a scaled pixel in an image basedon content characteristics of neighboring pixels in the image; means fordetermining an intensity (k) of a spatial variant interpolation filterbased on the symmetry A; means for adjusting the spatial variantinterpolation filter based on the intensity (k); and means for applyingthe spatial variant interpolation filter to interpolate the scaledpixel.
 44. The device of claim 43, wherein the adjusting means includesmeans for determining a warped distance (s′) based on the symmetry (A)of the scaled pixel and the intensity (k) of the filter response, andmeans for adjusting the spatial variant interpolation filter based onthe warped distance (s′).